It is known in the prior art to provide modular form elements which may be stacked end to end and wherein a plurality of horizontal courses are superposed one upon the other to create a wall of formwork. Examples of such elements are disclosed in U.S. Pat. No. 2,172,052 to Robbins and U.S. Pat. No. 3,788,020 to Gregori.
It is also known to provide modular form elements consisting of a plurality of vertical and essentially closed forms which can be nested alongside one another to create a series of adjacent concrete columns. U.S. Pat. No. 5,216,863 to Nessa et al. discloses such elements having generally circular or octagonal cross sections. In Nessa's octagonal cross section embodiment, the cross section of the form element comprises the general shape of an octagon with one side missing so as to create an open side. The free edges adjacent the open side are provided with retaining means which are designed to cooperate with complementary retaining means mounted on the back of an adjacent element. A plurality of elements can thereby be secured to one another, "piggyback" style, to create a formwork of columns into which concrete can be poured.
There are a number of desirable objectives in relation to modular form elements. Where it is intended to leave the form in place after casting the concrete, it is desirable to provide a form element which enables the easy application of wall finishes or coverings to the surface thereof. An important feature is the ability to allow the concrete to flow between interconnected form elements so so as to provide strength and rigidity to the concrete structure. It is also desirable to be able to insert reinforcing rods in the formwork. The formwork should be waterproof to prevent corrosion of reinforcing elements embedded in the concrete. It is also desirable for finished formwork to offer insulation properties.
Various prior art approaches achieve some of these objectives, but with varying success. For example, in the case of U.S. Pat. No. 5,216,863 it is difficult to provide insulation or liner within the form, mainly because of the essentially closed nature of the octagonal or circular form, and the structure of the form tends to impede the flow of concrete between adjacent forms. Moreover, the resulting formwork lacks structural rigidity and when the formwork is filled with concrete, it suffers from a "banana effect" which causes the walls of the form elements to bulge out. This makes it difficult to secure wall finishes and coverings.